1. Field of the Invention
The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer or the like with a grinding plate to a flat, mirror finish, and more particularly to a polishing apparatus with a mechanism for installing a grinding plate easily and reliably on a turntable.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller device and wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnections is photolithography. Though the photolithographic process can form interconnections that are at most 0.5 xcexcm wide, it requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small. It is therefore necessary to make the surfaces of semiconductor wafers flat for photolithography. One customary way of flattening the surface of semiconductor wafers on which integrated circuit devices are formed has been to polish semiconductor wafers with polishing a apparatus.
Heretofore, polishing apparatus for polishing planar workpieces, generally referred to as CMP (Chemical Mechanical Polishing) apparatus, comprise a turntable with a polishing pad attached thereto and a top ring for holding a planar workpiece to be polished. The top ring which holds a workpiece to be polished presses the workpiece against the polishing pad on the turntable. While an abrasive liquid is being supplied to the polishing pad, the top ring and the turntable are rotated about their own axes to polish the lower surface of the workpiece to a planar mirror finish. In particular, the planar workpiece to be polished is a device wafer with a circuit pattern formed thereon.
FIG. 1 of the accompanying drawings shows a conventional polishing apparatus. As shown in FIG. 1, the conventional polishing apparatus comprises a turntable 5 with a polishing pad 6 attached to an upper surface thereof, a top ring 1 for holding a semiconductor wafer 4 which is a workpiece to be polished while rotating and pressing the semiconductor wafer 4 against the polishing pad 6, and an abrasive liquid supply nozzle 9 for supplying an abrasive liquid Q to the polishing pad 6. The top ring 1 is connected to a top ring drive shaft 8, and supports on its lower surface a resilient mat 2 such as of polyurethane or the like. The semiconductor wafer 4 is held on the top ring 1 in contact with the resilient mat 2. The top ring 1 also has a cylindrical guide ring 3 mounted on a lower outer circumferential surface thereof and having a lower end projecting downwardly beyond the lower supporting surface of the top ring 1 for preventing the semiconductor wafer 4 from being dislodged from the lower surface of the top ring 1 while the semiconductor wafer 4 is being polished. The top ring 1 is tiltably supported on the lower end of the top ring drive shaft 8 by a ball bearing
In operation, the semiconductor wafer 4 is held against the lower surface of the resilient mat 2 on the top ring 1, and pressed against the polishing pad 6 by the top ring 1. The turntable 5 and the top ring 1 are rotated about their own axes to move the polishing pad 6 and the semiconductor wafer 4 relatively to each other in sliding contact for thereby polishing the semiconductor wafer 4. At this time, the abrasive liquid Q is supplied from the abrasive liquid supply nozzle 9 to the polishing pad 6. The abrasive liquid Q comprises, for example, an alkaline solution with fine abrasive grain particles of silica or the like suspended therein. Therefore, the semiconductor wafer 4 is polished by both a chemical action of the alkaline solution and a mechanical action of the fine abrasive grain particles. Such a polishing process is referred to as a CMP process.
The conventional CMP process in which the abrasive slurry of fine abrasive grain particles is supplied to the polishing pad suffers the following two problems.
The first problem is that the polished surface may not be fully planarized and may have undulations depending on the types of patterns and the states of steps on the polished surface. Generally, patterns on semiconductor wafers have various dimensions and steps. Some of the steps include smaller convexities and concavities spaced at a pitch of a few xcexcm and having heights ranging from 0.5 to 1 xcexcm, and larger convexities and concavities spaced at a pitch ranging from 100 xcexcm to 1 mm. When the surface of such a semiconductor wafer with those steps, which is covered with a film of silicon dioxide or aluminum, is planarized, both convexities and concavities of the pattern are polished such that the polishing rate is higher in regions where smaller convexities and concavities are present and lower in regions where larger convexities and concavities are present. As a result, large undulations are developed on the polished surface. The reason for such large undulations is that since the surface of the semiconductor wafer is chemically and mechanically polished by the relatively soft polishing pad of polyurethane or the like and the abrasive liquid, not only the convexities but also the concavities of the surface are polished.
The second problem is that the polishing apparatus incurs a high running cost and needs special care to avoid environmental contamination. The abrasive liquid comprises an alkaline solution with fine abrasive grain particles of silica or the like suspended therein, for example. In order to polish the semiconductor wafer to a highly uniform planar finish, the abrasive liquid needs to be supplied in a sufficient quantity onto the polishing pad. However, most of the supplied abrasive liquid does not contribute to the actual polishing operation, but is discharged as a waste liquid. Because the abrasive liquid used in polishing highly dense semiconductor wafers is highly costly, it makes the polishing process also highly costly. Furthermore, since the abrasive liquid is in the form of a slurry containing fine abrasive grain particles of silica or the like, its waste liquid requires special attention to keep the working environment clean. Specifically, a system for supplying the abrasive liquid and a system for discharging the waste liquid tend to be greatly contaminated, and a system for processing the waste liquid is highly complicated.
There is known a process of polishing semiconductor wafers with a grinding plate. The grinding plate, which is also referred to as a fixed abrasive polisher, comprises a flat plate of abrasive grain particles of silica or the like which are coupled together by a binder. The grinding plate is applied to a turntable, and a semiconductor wafer held by a top ring is pressed against the grinding plate and polished thereby in sliding movement relative thereto.
Since the grinding plate is harder than the polishing pad, only convexities on the surface of the semiconductor are polished, and the polished surface is free of any appreciable undulations and is sharply defined. As no slurry containing fine abrasive grain particles is used, the cost of the polishing process is lower, and any special care to avoid environmental contamination is not necessary.
A polishing apparatus which employs the grinding plate requires that the grinding plate and the turntable be fixed to each other easily and reliably.
A conventional polishing pad is attached to a turntable by an adhesive applied to the reverse surface of the polishing pad. The polishing pad is bonded to the turntable continuously from an end of the turntable while being elastically deformed in order not to trap air bubbles in the bonded surface. The bonded polishing pad can be peeled off from an end of the turntable while being elastically deformed.
A grinding plate, however, cannot be elastically deformed when it is installed on and detached from a turntable because the grinding plate is much more rigid than the polishing pad. Therefore, the grinding plate cannot directly be bonded to and peeled off the turntable with ease and efficiency.
The polishing pad is usually bonded to the turntable by preparing a polishing pad blank larger in diameter than the turntable, bonding the polishing pad blank to the turntable, and then cutting off any excessive end portion of the polishing pad blank to leave a polishing pad, of the same diameter is as the turntable, bonded to the turntable. This bonding process is employed because, if a polishing pad of the same diameter as the turntable were initially bonded to the turntable, then the efficiency would be poor because the desired positional accuracy of the polishing pad with respect to the turntable would not easily be achieved. The grinding plate cannot be installed on the turntable according to the above process since the grinding plate, which is much harder than the polishing pad, cannot easily be cut off and cannot be handled efficiently on site. Accordingly, the grinding plate needs to be fixed to the turntable with high positional accuracy and efficiency according to a process other than the conventional bonding process.
It is therefore an object of the present invention to provide a polishing apparatus with a grinding plate that can easily and reliably be installed on and detached from a turntable.
According to an aspect of the present invention, there is provided a polishing apparatus comprising a turntable, a grinding plate tool fixedly mounted on the turntable and including a grinding plate, holding means for holding a workpiece to be polished and pressing the workpiece against the grinding plate in sliding contact therewith for polishing a surface of the workpiece to a flat, mirror finish, and a clamping mechanism for fixing an outer circumferential portion of the grinding plate tool to the turntable.
According to another aspect of the present invention, there is provided a polishing apparatus comprising a turntable, a grinding plate tool fixedly mounted on the turntable and including a grinding plate, and holding means for holding a workpiece to be polished and pressing the workpiece against the grinding plate in sliding contact therewith for polishing a surface of the workpiece to a flat, mirror finish, the turntable having a plurality of interconnected holes defined therein for developing a vacuum between the grinding plate and the turntable to attract the grinding plate fixedly to the turntable.
According to still another aspect of the present invention, there is provided a polishing apparatus comprising a turntable, a grinding plate tool fixedly mounted on the turntable and including a grinding plate, the grinding plate tool being made of a magnetic material, holding means for holding a workpiece to be polished and pressing the workpiece against the grinding plate in sliding contact therewith for polishing a surface of the workpiece to a flat, mirror finish, and a magnet disposed in the turntable for magnetically attracting the grinding plate tool fixedly to the turntable.
According to yet another aspect of the present invention, there is provided a polishing apparatus comprising a turntable, a grinding plate tool fixedly mounted on the turntable and including a grinding plate, holding means for holding a workpiece to be polished and pressing the workpiece against the grinding plate in sliding contact therewith for polishing a surface of the workpiece to a flat, mirror finish, and a stopper pin disposed between the grinding plate tool and the turntable and fixing the grinding plate tool to the turntable.
Since the grinding plate is fixed to the turntable by any of the various members, the grinding plate can easily and reliably be installed on and detached from the turntable. The polishing machine with the grinding plate can be operated highly efficiently. The grinding plate can polish the workpiece to a sharply defined finish at a reduced cost without the need for special care to avoid environmental contamination.
Since the grinding plate can easily and reliably be replaced with a new one, the lead time in a polishing process carried out by the polishing apparatus can be reduced. Because the grinding plate can be selected and replaced as desired to meet the properties of the workpiece to be polished, it is possible to use a wide variety of grinding plates of various polishing characteristics to satisfy various polishing needs. As a result, various workpieces can be polished in an optimal fashion matching the properties thereof.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.